Display devices generally display information to a viewer. The performance of a display is described in terms of various characteristics of the display. One such characteristic is the ability of the display to absorb ambient light originated from various sources of light such as a light bulb in a room or on a street or the sun. Generally, ambient light that is incident on a display and not absorbed by the display is superimposed on the displayed information resulting in reduced contrast. The reduced contrast due to ambient light is generally referred to as washout. Washout is especially a concern in applications where the ambient light is very bright. For example, in outdoor applications, ambient light from the sun can significantly reduce the display contrast making it difficult for a viewer to discern the displayed information. A display, such as an instrument panel used in a motor vehicle, is particularly susceptible to washout from sun light. Typically, instrument panels in a motor vehicle are recessed in a housing to reduce ambient light access to the display. The housing is generally made black to further reduce washout by reducing the amount of light that is reflected by the housing.
Another characteristic of a display is the viewing angle. It is generally desirable that the displayed information be easily viewable over a predetermined range of viewing angles. In some cases, it is further desirable that the displayed information not be viewable outside a predetermined viewing range. In other words, it may be desirable to limit the viewability of a display to a particular and intended viewing position. For example, limiting the display viewability may be desirable for privacy considerations. Another setting where such limitation may be desirable is where viewability of the display by a person located outside the intended viewing position may interfere with the person's ability to perform a given task. For example, in a motor vehicle, it may be desirable that a display or an instrument cluster be viewable by the driver but not by the other passengers as it may interfere with their comfort. Reflection of light that originates from an instrument display off of a windshield, a side window, or other glossy surfaces in a motor vehicle can be distracting to a driver. Typically, the recessed housing of an instrument cluster in a motor vehicle is designed to limit the viewing angle of the displayed information.
Another characteristic of a display is the overall footprint. Displays are generally desirable to have minimized depth in order to reduce the depth and/or the overall volume of the display. For example, in the case of an instrument panel in a motor vehicle, it may be desirable to minimize the recess in the instrument housing in order to save space or, for example, make room for accessories. As one display characteristic is improved, one or more other display characteristics often degrade. As a result, certain tradeoffs are made in a display device in order to best meet the performance criteria for a given display application. Thus, there remains a need for displays with improved overall performance while meeting the minimum performance criteria.